This invention relates to biologically important synthetic Growth Hormone Releasing Hormone complementary peptides and antibodies thereto.
Growth Hormone Releasing Hormone (GHRH), also known as Growth Hormone Releasing Factor, is a hypothalamic peptide which positively regulates the synthesis and secretion of growth hormone in the anterior pituitary. GHRH was originally isolated and structurally characterized from human pancreatic tumors that caused acromegaly. Since then, GHRH has been isolated from several different species, including rat, pig, cow, man, sheep, and goat (Bohlen et al., Biochem. Biophys. Res. Comm. 125: 1005-1012, 1984).
GHRH has been widely studied. The amino acid sequence of rat hypothalamic GHRH has been determined (Bohlen et al., 1984, supra). Also, the cDNA to rat GHRH has been reported (Mayo et al., Nature 314: 464-467, 1985). Human GHRH is reported to have high homology with rat GHRH and a GH-stimulating effect on the rat pituitary gland (Baird et al., Neuroendocrinology 42: 273-276, 1986). Ling et al., Biochem. Biophys. Res. Comm. 123: 854-861, (1984) tested the capacity of a series of C-terminal deleted analogs of synthetic human GHRH to release growth hormone and report that the minimal biologically important core of GHRH with full intrinsic activity comprises the fragment (3-21).
Biro suggested (Biro, Medical Hypotheses, 7:969-1007, 1981) that protein-protein interactions are based on binding of restricted portions of the proteins that are primarily formed by "informational complementary (ic)" amino acids. He also suggested that these specific complementary amino acids are encoded by complementary DNA sequences; further, interaction between complementary amino acid sequences would occur both in parallel and in antiparallel alignment of the peptides. Although Biro (1981) investigated only the 5'-3' direction, his data also support the significance of the 3'-5' direction by emphasizing the importance of palindrome nucleic acid sequences in encoding the specifically interacting peptide sequences.
Model peptides designed to have minimal homology to the naturally occurring peptide but having the same hydropathic pattern have been demonstrated to exhibit biological activity (See, e.g., Kaiser and Kezdy, Science, 223: 249-255, 1984). Blalock and Smith reported that codons for hydrophilic and hydrophobic amino acids on one strand of DNA are complemented by codons for hydrophobic and hydrophilic amino acids on the other DNA strand, respectively, and that codons for slightly hydrophilic ("uncharged") amino acids are complemented by codons for amino acids of the same character (Biochem. Biophys. Res. Comm. 121: 203-207, 1984). These workers theorize that the two complementary strands of the DNA encode two peptides having hydropathic anti-complementarity. It has been reported that the hydropathic anti-complementarity of a number of amino acids (and hence that of the peptides) based on the genetic code occurs when complementary codons are read in the 5'-3' as well as in the 3'-5' direction (Bost et al., Proc. Natl. Acad. Sci. 82: 1372-1375, 1985a; Bost et al., Biochem. Biophys. Res. Comm. 128: 1372-1380, 1985b; Blalock and Bost, Biochem. J. 234: 679-683, 1986).
Bost et al., 1985a, supra, have reported that a peptide ("HTCA") corresponding to the complementary (5'-3') RNA sequence of ACTH (1-24) mRNA is capable of binding synthetic ACTH as determined by ELISA. Blalock and Bost, supra, have reported that both 3'-5' and 5'-3' complementary peptides bind .sup.125 I-ACTH in a solid phase binding assay. Similar binding was reported for 5'-3' complementary peptides of .gamma.-endorphin (Bost et al., 1985a, supra). Antibodies raised against the complementary peptide, HTCA, have been reported to stimulate corticosterone secretion of adrenocortical cells in vitro (Bost et al., 1985a, supra). It is also reported that, using the same antibodies in immune affinity chromatography, the ACTH-receptor was purified and its molecular structure and .sup.125 I-ACTH binding characteristics were determined (Bost and Blalock, Molec. Cell. Endocrinol. 44: 1-9, 1986). According to Bost et al., 1985b, supra, messenger RNA sequences complementary to the mRNA sequences for the receptors of epidermal growth factor (EGF), interleukin-2 (IL-2) and transferrin (TF) encode peptides having high homologies with the amino acid sequence of their respective ligands, if the transcription is carried out in 3'-5' direction. Gorcs et al., Peptides, 7: 1137-1145 (1986) report possible recognition of the GnRH receptor by an antiserum against a peptide encoded by nucleotide sequence complementary to mRNA of a GnRH precursor peptide.
GHRH peptides have applications to the fields of animal husbandry, clinical medicine and basic research. For example, it was determined that administration of human GHRH to lactating holstein cows increases the secretion of growth hormone consistently and causes an apparent increase in feed to milk conversion (Enright et al., J. Dairy Sci. 69: 344-351, 1986). GHRH peptides are useful in vitro, e.g., as unique research tools for understanding how growth hormone secretion is regulated at the pituitary level and are also be useful in vivo, e.g., to treat symptoms related to growth hormone deficiencies, to increase the rate and extent of growth in commercial animals, to increase milk yield in commercial animals.